1. Field of the Invention
This invention relates to a process for the production of a cycloolefin random copolymer. More specifically, it relates to a process for the production of a cycloolefin random copolymer, which permits the production of a cycloolefin-based random copolymer having a high molecular weight at a high yield.
2. Prior Art
A copolymer of ethylene and a specific bulky cycloolefin is a synthetic resin whose optical, mechanical and thermal properties are well balanced and used in the field of optical materials such as optical memory disks and optical fibers. It is already known that such a cycloolefin copolymer can be produced by copolymerizing ethylene and cycloolefin using a catalyst formed from (i) a transition metal compound, (ii) an organic aluminum oxy compound and/or a compound capable of forming an ionic complex when it reacts with a transition metal compound, and (iii) an organic aluminum compound as required. The copolymerization in such a catalytic system is usually carried out in a solvent having a high solubility parameter, such as toluene or benzene. However, when a cycloolefin copolymer having high heat resistance is to be synthesized in such a solvent, the proportion of the cycloolefin based on the total concentration of monomers in a polymerizer must be increased. Therefore, when .alpha.-olefin is ethylene, for example, it is impossible to raise the partial pressure of ethylene, thereby causing such problems as a reduction in polymerization speed, an incomplete reaction, and a large volume of cycloolefin to be recovered after polymerization.
When a cycloolefin copolymer is to be synthesized in a solvent having a high solubility parameter in a high concentration, namely, 80 g/l or more, the viscosity of a polymerization system becomes high, thereby making it difficult to remove polymerization heat and maintain the uniform distribution of monomer components in the polymerization system, and lowering the transportability of a polymer solution.